The present invention relates to an information delivery system for delivering digital information transmitted through a broadcasting network or a communication network to a plurality of terminal devices, especially, to a stream distribution system which handles stream data.
In recent years, due to the spread of the digital broadcasting network and the communication network (including a computer network) which includes digital satellite broadcasting and CATV, etc., a so-called information delivery system is proposed to provide various information, that is, multimedia information to many and unspecified homes (hereafter, called a user). Here, multimedia information means digital information on the video, the static image, and the voice, etc. In this digital information, information, which especially includes a video, a voice, a static image, and character information, etc., and requires a real time characteristic, is called stream data. This stream data is handled in distinction from digital information composed only of a static image and character information.
To achieve such an information delivery system, a local area server which is called a set-top box (STB) and/or an IRD (Integrated Receiver Decoder) is proposed. The personal computer connected with a television set and a communication network is handled as a terminal device for the local area server.
A preferable construction is as follows as the information delivery system. That is, it is desirable that the information delivery system is constructed as being arranged in each home, being connected with a plurality of terminal devices such as television sets and personal computers, and receives plural kinds of stream data transmitted through the digital broadcasting network and the communication network and sends it to each terminal device. Plural kinds of stream data includes video stream (VS) from video on demand (VOD) system which uses the communication network etc. besides said digital broadcasting stream (BS).
In such a system, the user arbitrarily selects information (program and title, etc.) which he/she wants to attend from among broadcasting stream (BS) and video stream (VS) to be able to reproduce the information on the display of the terminal device.
As mentioned above, the user selects desired information on the demand from various stream data by the information delivery system to be able to attend the information. By the way, the content of the transmitted program has changed hourly especially in the broadcasting stream. Therefore, there is a possibility to overlook a program with a high demand started in another channel (for example CATV), when, for example, an attention of the stream of the channel (for example satellite broadcasting) which the user selected is done. In this specification, a term “attention (attend)” means that the stream data is received, decoded, and reproduced at the terminal device.
There is a possibility that a similar state is generated in case the user first attends the stream of VOD. To prevent such a state, the stream not selected by the user is monitored as a background, and when the attention priority of the user changes, a method of switching the stream of the selected attention and the background stream is proposed. Here, the data transmission band (sending band to the terminal device) is usually limited in the system like the local area network which includes said local area server. This data transmission band (or, only called “band”) means an amount of the transmission data per unit time (bps: bits per second).
Since there is a band limitation like the above-mentioned, it is necessary to prepare the distribution option having a narrow band for each channel of the broadcasting stream (Or, channel of the VOD stream). Then, by using this distribution option having a narrow band, the method of simultaneously displaying channels on a display of the terminal device by mixing the stream of each channel is proposed.
However, the picture quality at attending the stream relatively becomes low when the band is narrow. To attend the stream which the user demands by the high picture quality, it is necessary to reset the band of the corresponding stream, but the operation procedure is complex. It is not actually easy even though it is preferable to be able to change the band distribution of each channel continuously and arbitrarily.